Conventional pneumatic radial tires have such a structure of the bead portion in which a portion in the vicinity of respective ends of a carcass layer is folded back and turned up around the corresponding one of a pair of annular bead bundles from inside to outside of the tire, and in order to reinforce the vicinity of a turnup portion of the carcass layer located in the bead portion, more than two reinforcing layers are arranged to cover the turnup portion, and the tires have various combinations of the height of the end of the reinforcing layers and the height of the end of the turnup portion of carcass layer, measured from the bead base.
FIG. 9 of the accompanying, drawings shows an example of conventional radial tires. In FIG. 9, the reference numeral 1 denotes a bead portion. A portion in the vicinity of respective ends of a carcass layer 2 comprising metal cords arranged at substantially 90.degree. to the circumferential direction of the tire is folded back and turned up around or about the corresponding one of a pair of annular bead bundles 4 from inside to outside of the tire, to form a turnup portion 2a. Above the bead bundle 4 sandwiched between the turnup portion 2a and a main portion of the carcass layer 2 leading to the turnup portion, there are incorporated a lower bead filler 5a and an upper bead filler 5b. Also, externally to the turnup portion 2a, two reinforcing layers are disposed, which comprise a steel cord reinforcing layer 3a and a fiber cord reinforcing layer 3b. On the outer side of the fiber cord reinforcing layer 3b, a rubber layer 7 is disposed so as to protect an upper end portion of the reinforcing layer 3b. The height h.sub.1 of the upper end of steel reinforcing layer 3a immediately adjacent the turnup portion 2a, measured from the bead base, is lower than the height h.sub.0 of the upper end of the turnup portion 2a from the bead base, which in turn is lower than the height h.sub.2 of the upper end of the fiber cord reinforcing layer 3b from the bead base (h.sub.1 &lt;h.sub.0 &lt;h.sub.2). The elastic modulus at 100% elongation (hereinafter abbreviated as elastic modulus) of each of the lower bead filler 5a, the upper bead filler 5b and the rubber layer 7 is 4 to 7 MPa.
For radial tires of such conventional structuring, there have been proposed a variety of combinations of the end heights h.sub.1 and h.sub.2 of the reinforcing layers and the end height h.sub.0 of the turnup portion 2a, but it still is frequently experienced that in the vicinity of the end of the turnup portion 2a or the end of each reinforcing layer, a separation trouble occurs, which tends to develop to reach a surface region of the bead portion to give rise to a crack damage.
Thus, in order to enhance the durability of the bead portion, various proposals have been made, for example such as to make optimum the height h.sub.0 of the upper end of the turnup portion 2a of the carcass layer, to incorporate a further reinforcing layer, to define an optimal combination of the end heights of the turnup portion and the reinforcing layer and/or to incorporate a rubber layer between the turnup portion 2a of the carcass layer and an end portion of the steel cord reinforcing layer 3a. By way of an example, FIG. 10 of the accompanying drawings shows the structure of the bead portion according to Japanese patent application Kokai Publication No. 58-112808. In FIG. 10, a rubber stock 6 is disposed immediately inner to the fiber cord reinforcing layer 3b, and an upper end portion of each of the turnup portion 2a and the steel cord reinforcing layer 3a is covered with the rubber stock 6. The elastic modulus of the rubber stock 6 is higher than the elastic modulus of each of the lower bead filler 5a, the upper bead filler 5b and the rubber layer 7. However, the above proposals are directed mainly to the cancellation of the separation trouble between the turnup portion 2a of the carcass layer and the end portion of the steel cord reinforcing layer 3 a, and although according to the proposed methods there have been brought about a remarkable result in respect of the intended suppression of the separation trouble between the turnup portion and the steel cord reinforcing layer, as a result thereof there has now come to be more noticeable than before a separation trouble in an end portion of the fiber reinforcing cord layer 3b, to which attention has not much been paid before.
The present invention has for its object to provide a pneumatic radial tire with which the generation of a separation trouble between the turnup portion of the carcass layer and an end portion of the steel cord reinforcing layer is suppressed and the separation trouble in an end portion of the fiber cord reinforcing layer is obviated so that the bead portion can exhibit a more fully satisfactory durability.